Automotive radar systems are seen as a crucial element to increase road safety and driver comfort. The first generation of automotive radar systems targeted automatic cruise control and parking aid applications. Such a radar system 100 is shown schematically in FIG. 1. It comprises three main sections: transmit section 110, a receive section 120 and a control and processing section 130. The transmit section 110 comprises a high-frequency chirp generator 111, which produces a frequency modulated continuous wave (FMCW) at a frequency which may be, for instance, 24 GHz. The chirp signal is supplied to a phase locked loop (PLL) 112, and then frequency tripled in a frequency tripler 113 to provide a signal 141. The signal 141 is amplified by a power amplifier 114, and fed, via an antenna output connector 115, to be transmitted by a transmit aerial or antenna (not shown) as a radar signal. In the presence of a reflective object, a reflected radar signal may be received by one or more receive aerials or antenna (not shown), and input via one or more antenna input connectors 126, to the receive section 120. In the figure two receivers are shown, although it will be appreciated that the system may comprise a different number of receivers, such as one or three. Each received signal is amplified by a low noise amplifier 125 and down-converted by being mixed with a copy of the transmitter tripler output signal 141 in mixer 124. Each down-converted signal is filtered by filter 123, and digitised and dumped to a digital signal processor 131, by an analog-to-digital converter (ADC) 122. The digital signal processor 131 forms part of the control and processing section 130. The control and processing section 130 also includes a clock generator 132 for providing a clock function, together with a microprocessor and timing reference device 133 for providing appropriate timing signals. The output from the radar system may be communicated with other electronics within the automobile over a controller area network (CAN) bus 160.
In summary, then, in typical car radar systems—using “car” as an example of the automotive application field—a signal, modulated according to a specific waveform principle, is transmitted at a predetermined carrier frequency. The reflected signals are down-converted to baseband signals by the analogue receiver and processed by the digital part of the system. In these processing steps one or more of the distance to an object, the relative radial velocity, that is to say, the velocity at which the object is approaching the car, and the angle between the object and the car are calculated.
As mentioned, the modulation system described above is frequency modulated continuous wave (FMCW). FMCW is a suitable waveform for automotive radar systems due to its accuracy and robustness. In particular, the implementation in which a sequence of short duration frequency chirps is transmitted has favorable properties, for detecting objects moving with a non-zero relative radial velocity.
In FMCW based radar system the radial distance to a reflecting object is converted to a sine wave oscillating at a beat frequency determined by the slope of the frequency ramp and the time of flight to the object. It is up to the digital baseband to estimate the frequency of the sine wave; in preferred implementations this may be done by a Fast Fourier Transformation (FFT).
Modern automotive radar systems combine a high resolution with a long measurement range. As a consequence the resulting number of data points and thus required processing power is high. In addition a large number of successive measurements (chirps) are required to achieve a high relative radial velocity resolution.
Recently new applications such as EBA (Electronic Brake Assist), blind spot detection and rear cross traffic alert have started to be introduced. It is expected that in the near future several radar systems will be used to cover the whole 360° around the car. These radar systems will not be identical; each application has a different set of requirements. These requirements include (but are not limited to) distance resolution and angular resolution. The development of specialized integrated circuits (ICs) for every radar application will significantly increase the cost of a complete 360° radar solution.
As mentioned, measuring the angle of arrival to an acceptable degree of resolution may be important: the combination of the angle of arrival and the distance allows the system to project the estimated location of an object in a Cartesian or polar coordinate system. To be able to estimate this angle accurately multiple transmit and/or receiver antennas may be required. In addition each antenna has its own analogue transmitter and/or receiver and ADC. The calculation of the angle of arrival is executed in the digital part of the system. Different calculation methods, known in the art, may be used.
Currently automotive radar products and systems are based upon multiple chips each with one or more functions. (Herein, the terms “chips” and “ICs” shall be considered as interchangeable, both referring to semiconductor-based Integrated Circuits.) These systems generally have in common that the radio frequency (RF) circuits are realized on a different IC than the signal processing IC. Therefore multiple RF modules can be combined with a powerful signal processor to realize a system with longer measurement range and higher angle of arrival resolution. This gives the manufacturer the possibility to cover multiple radar applications. However, this requires an assembly of different ICs, which thus may add to the cost of the radar system overall.
In a radar system where the analogue parts and the digitals parts consist of different ICs multiple receivers and/or transmitter may be connected to one or more digital signal processors. In this way the angular resolution and measurement range can be extended. Radar systems where the analogue transmitter and receiver are combined with a digital signal processor on a single IC in order to avoid the above-mentioned assembly costs generally have a limited angular resolution due to the limited number of antennas. Since the functionality of the IC is fixed after production several different ICs then have to be developed to cover all required applications.
It would be desirable to develop a radar system which suffered to a lesser extent from one or more of the problems described above.